The printing of microimages on microfiche cards and the use of viewers for illuminating, enlarging, projecting an displaying selected frames of the cards on a viewing screen is well known in the art. The printing of microimages on filmstrips and the use of viewers for illuminating, enlarging, projecting and displaying selected frames of the filmstrip on a viewing screen is also well known in the art.
It is further known to house the filmstrip on a cassette for presenting a length of flexible film for projection and display. By storing information on a microfilmstrip, an entire book or a lengthy catalog of parts may be stored on a single compact cassette. The prior art, as evidenced by U.S. Pat. No. 3,700,321, has fixedly located a generally U-shaped cassette with a microimage holding bight portion window between an illuminating system and a lens assembly to precisely align a selected microimage with the optical system of the viewer.
There exist countless situations in which it would be advantageous to store a greater number of microimage frames on a single filmstrip. For example, it is desirable to store a full set of volumns of a given reference or the entire inventory of a given company within a single cassette. To this end, previous patents such as U.S. Pat. No. 3,319,517 have provided a cassetted filmstrip, the transverse dimension thereof being great enough to include a plurality of rows of microimages so as to substantially increase the amount of printed matter that can be stored in a single cassette.
As the width of the cassetted filmstrip was increased, it became necessary to modify existing viewer-cassette assemblies to accept, project and display selected microimage frames regardless of their longitudinal or transverse location on the filmstrip. Early microfiche viewers provided for manual movement of a fiche supporting table in both transverse and longitudinal directions to align a selected microimage between a lower source of illumination and an upper projection lens system. As technology advanced and 8 and 16 mm cassetted microfilm supplanted microfiche, there was no need to traverse the width of the film. Because the transverse dimension of the filmstrip was relatively small, its full width could be projected onto the viewing screen.
With the continuing development of microfilm technology came the advent of wider microfilmstrips. As the full filmstrip width could no longer be displayed on the viewing screen at one time, it became necessary to incorporate a transverse filmstrip scanner into the viewer assembly. One type of scanner was developed in U.S. Pat. No. 3,319,517. The scanner basically included a transport assembly on which the film spools were secured for slidable movement relative to a lens projection assembly. However, the filmstrips of that and other prior art devices were not housed in a cassette and therefore were easily scratched and otherwise injured by the constant human handling necessary to prepare the filmstrip for projection.
It is accordingly a major purpose of the present invention to provide a cassette for housing and transporting filmstrips having transverse dimensions great enough to house a large number of microimage frames thereacross and to provide a viewer having a movable carriage in which the cassette is placed for scanning and projecting those transverse microimage frames.
Of course, the filmstrip length is many times greater than its width. With this in mind, prior viewer systems incorporated drive assemblies for the selective longitudinal transportation of the filmstrip within the cassette. However, none of the previous systems employed a movable carriage for transversely scanning the width of a cassetted filmstrip.
It is yet another object of the present invention to provide a viewer having a movable carriage for holding a cassette and in which the drive means for transporting the filmstrip and presenting selected longitudinal microimage frames for projection are mounted on the carriage for movement therewith.
Many previous viewers for projecting and displaying filmstrips such as the viewer shown in U.S. Pat. No. 3,319,517 have tensioned the filmstrip over a plastic plate so as to hold the filmstrip in the focal plane of the objective projecting lens. But the constant contact between the filmstrip and the plate often caused scratching or other injury of the filmstrip which seriously interfered with the projected image because of the optical magnification occasioned by the viewer. Other viewers held the filmstrip in the focal plane by supporting the longitudinal edges thereof in the area about the optical path of projected light. Of course, as the width of the film increased, such support means failed to adequately maintain the entire filmstrip width under sufficient tension, thereby having sections thereof buckle out of the focal plane.
One additional object of the present invention is to provide a pair of transparent glass plates between which a filmstrip, regardless of width, may be disposed in non-contacting positions for longitudinal movement without contacting either plate and which plates cooperate with a lens assembly housed in the viewer to clamp the entire width of the filmstrip between the plates into a focusing plane only when the filmstrip is not being moved.
These as well as further objects and advantages will become apparent from the detailed explanation of the invention that is provided in the description and claims, and is illustrated in the accompanying drawings.